This invention relates to coded-access, security systems having broad generalized application.
One particular application of such security systems is in anti-theft arrangements for placement within vehicle engine ignition circuits such that the ignition circuit cannot be actuated except through the use of a coded signal and baud rate known only by an authorized driver of the vehicle. In most prior art systems along these lines, a code transmitter is wired into the engine ignition circuit, while in others the code transmitter comprises a radio transmitter which broadcasts a coded signal to the receiver which is wired into the engine ignition circuit.
Earlier efforts along the above lines have made exclusive use of radio frequencies and, to the knowledge of the inventors, have not made use of the possibilities inherent in the use of infrared.
The prior art, as best known to us, is represented by U.S. Pat. Nos. 4,240,516 (1980) to Henderson, 4,413,261 (1983) to Greenberg, and 4,143,368 (1979) to Route. None of these patents or other art known to us, employs modulated infrared light. This approach, in addition to avoiding the need for approval by the Federal Communications Commission, makes possible a higher degree of precision and, thereby, reliability of operation. Also, a higher number of digital code combinations can be attained without any corresponding increase in design complexity. The use of a programmable baud rate increases the security level of the system by yet further orders of magnitude.